Collagen-induced arthritis is a well-established experimental animal model of arthritis that has been used to gain insight into the pathogenesis of rheumatoid arthritis. The overall objective of this proposal is to identify the non-MHC genes that regulate development of this form of experimental arthritis. In experiments that led up to present proposal, advantage was taken of the fact that two inbred rat strains sharing the same MHC haplotype, RT1av1, differed strikingly in their susceptibility to arthritis induced with homologous rat type II collagen, although both strains exhibited the production of collagen autoantibodies. A genome-wide scan in a F2 cross between arthritis-susceptible DA and arthritis-resistant ACI rats identified one non-MHC DA- originated quantitative trait locus (QTL), Cia7, on rat chromosome 2, and two other suggestive loci on chromosome 2 and 10. A significant sex effect was also identified. These three loci map to genomic intervals syntenic to regions previously identified in the mouse and human genomes containing genes involved in the susceptibility to different forms of autoimmune diseases, further emphasizing the relevance of this study. This proposal hypothesizes that the three QTL described above contain genes that act to convert the state of asymptomatic autoimmunity induced by the collagen immunization into a frank autoimmune disease. The first aim is construction of genotype-guided speed congenic rats, introducing DA segments into ACI background, and vice-versa. Sex interaction with the three QTL will be studied in the congenic animals. At later stages, polycongenic rats will be generated to determine the interaction of the three loci. The second aim is identification of the genes. In order to accomplish this goal, two basic approaches will be used. First, a candidate gene strategy will be employed, taking advantage of mouse and human genome homology mapping data, and screening candidate gene exons for mutations, followed by sequencing, when applicable. Differential expression of certain candidate genes will be analyzed in cDNA libraries generated from synovial tissue and T cells. The second strategy will follow a more standard approach, first narrowing the congenic interval to 1 cM through generation of recombinants, followed by isolation of transcripts in the regions, cloning and sequencing. Both of these strategies will be supplemented by identification of candidate surrogate immunologic sub-phenotypes involved in the response that should provide both insight into the mechanism of gene action and alternative markers for immunologic phenotypes thus facilitating the gene discovery process.